C-1 inhibitor prevents non-specific plasminogen activation by a prourokinase mutant without impeding fibrin-specific fibrinolysis

ABSTRACT

A mutant prourokinase plasminogen activator (M5) was developed to make prouPA less subject to spontaneous activation during fibrinolysis. C1-inhibitor complexes with tcM5. The effect of C1-inhibitor on fibrinolysis and fibrinogenolysis by M5 was determined. Supplemental C1-inhibitor restores the stability of M5 but not that of prouPA. Clot lysis by M5 with supplemental C1-inhibitor showed no attenuation of the rate of fibrinolysis, whereas fibrinogenolysis was prevented by C1-inhibitor. Due to higher dose tolerance of M5 with C1-inhibitor, the rate of fibrin-specific lysis reached that achievable by nonspecific fibrinolysis without inhibitor. Plasma C1-inhibitor stabilized M5 in plasma by inhibiting tcM5 and thereby non-specific plasminogen activation. At the same time, fibrin-specific plasminogen activation remained unimpaired. This unusual dissociation of effects has significant implications for improving the safety and efficacy of fibrinolysis. Methods of reducing bleeding and non-specific plasminogen activation during fibrinolysis by administering M5 along with exogenous C1-inhibitor are disclosed.

RELATED APPLICATIONS

This application is a continuation-in-part of prior U.S. applicationSer. No. 11/472,607, filed Jun. 22, 2006, herein incorporated byreference.

BACKGROUND OF THE INVENTION

Existing thrombolytic drugs, used in the treatment of thromboembolicdiseases, have limited effectiveness and also carry the risk ofrethrombosis and hemorrhagic complications. Clinical experience withplasminogen activators has highlighted problems with both efficacy andside effects, particularly hemorrhage [Rao et al. J Amer Coll Cardiol.11: 1-11 (1988); Fennerty et al. Chest. 95: 88S-97S (1989)]. Becauseboth endpoints are dose-related, the efficacy of therapeuticthrombolysis has always been handicapped by its side effects.

Currently most therapeutic thrombolysis is performed using tissueplasminogen activator (tPA) and its derivatives. TPA can havehemorrhagic side effects. For example, tissue plasminogen activator(tPA) at a dose of 150 mg has been shown to induce superior coronarythrombolysis, but has been accompanied by an unacceptable incidence ofintracranial hemorrhage, obliging the adoption of a less effective doseof 100 mg [Braunwald et al. J Amer Coll Cardiol. 9: 467 (1987);Grossbard. J Amer Coll Cardiol. 9:467 (1987)].

Similarly, the other natural plasminogen activator, single-chainurokinase plasminogen activator (prouPA), a proenzyme, requires highinfusion rates for effective coronary thrombolysis which causesplasminemia and results in conversion of single to two-chain uPA (tcuPA)and bleeding [Meyer et al. Lancet 1:863-868 (1989)].

The bleeding complications of therapeutic thrombolysis have beenascribed to the direct lysis of hemostatic fibrin at a vascular injurysite and to the hemorrhagic diathesis caused by non-specific plasmingeneration resulting in fibrinogenolysis, degradation of fibrinogen andof clotting factors V and VIII. Fibrinogen is the principal proteinconstituent of a fibrin clot; clotting factor V is a cofactor in thecoagulation system, the lack of which causes a predisposition forhemorrhage; and clotting factor VIII is an essential clotting factor,the lack of which causes Hemophilia A.

Both tPA and prouPA are fibrin-specific in that they preferentiallyactivate plasminogen bound to fibrin over free plasminogen. Atphysiological concentrations, plasminogen activation by tPA and prouPAis fibrin-dependent and confined to the clot environment by plasmainhibitors. But, at therapeutic concentrations, the fibrin selectivityof tPA and prouPA is compromised, largely due to the fact that theseconcentrations are in excess of inhibitors, particularly plasminogenactivator inhibitor-1 (PAI-1), their principal plasma inhibitor. Theintrinsic activity of prouPA at therapeutic concentrations wassufficient to activate plasma plasminogen, which converted single-chainprouPA to two-chain uPA (tcuPA). Since tcuPA is a non-specificplasminogen activator, the fibrin-specificity of prouPA is lost. ThusprouPA's specificity depends on its plasma stability which allows tcuPAand plasmin generation to be confined to the fibrin clot [Pannell andGurewich, Blood, 67: 1215-1223 (1986)]. The systemic activation ofplasma plasminogen results in the generation of systemic tcuPA andundermines the therapeutic use of prouPA.

At therapeutic concentrations, prouPA is especially vulnerable tonon-specific plasmin generation since this results in loss of itsproenzyme configuration due to its conversion to tcuPA, a non-specificactivator, which, being an enzyme, then amplifies systemic plasmingeneration several hundred fold.

This cycle of reactions is initiated by the relatively high intrinsicactivity of prouPA which at therapeutic concentrations triggersplasminogen activation. Therefore, a prouPA mutation (M5) with a lowerintrinsic catalytic activity was developed. A five-fold reduction inintrinsic activity was achieved by a site-directed single residueexchange on a flexible loop in the catalytic domain (Lys3000→His) ofprouPA [Liu, et al. Biochemistry 35: 14070-14076 (1996)]. This produceda corresponding degree of improvement in plasma stability or inertnessat therapeutic concentrations. Unexpectedly, after activation totwo-chain M5 (tcM5), the mutant had a two-chain activity almost twicethat of tcuPA [Sun et al., J Biol. Chem. 272: 23818-23823 (1997)],consistent with their two-chain active catalytic sites also beingfunctionally distinct. U.S. Pat. No. 5,472,692 describes prouPA mutantsand the disclosure is incorporated herein by reference.

M5 induced efficient, fibrin-specific clot lysis in a plasma milieu invitro and in dogs with venous thromboemboli in which M5 was associatedwith no more bleeding than placebo [Liu et al. Circ Res. 90: 757-763(2002)] In a second animal study of M5, a more challenging arterialthrombus was selected and M5 was administered by a bolus/infusionadministration modeled on the clinical administration of prouPA or tPA.Because blood loss from injury sites was the side effect of mostconcern, a more quantitative measure of blood loss was used.Furthermore, the plasma inhibition of tcM5 was studied and found to berelated to a plasma inhibitor novel for tcuPA. M5 and tPA inducedcomparably effective lysis, but blood loss from fresh hemostatic siteswas ten-fold higher with tPA, suggesting that M5 spared hemostaticfibrin at doses which lyse intravascular clots [Pannell et al. Blood.69: 22-26 (1987)]. A difference in the lytic sensitivities of hemostaticversus intravascular fibrin to M5 was related to differences in themechanisms of fibrin-dependent plasminogen activation by the twoactivators [Gurewich et al. J Thromb Haemost. 4: 1559-65 (2006)].Specifically, M5 selectively activated plasminogen on partially degraded(fibrin fragment E) and not on intact fibrin, whereas tPA targetedplasminogen on intact fibrin (fibrin fragment D) [Liu et al. J ClinInvest. 88: 2012-2017 (1991)], which corresponds to hemostatic fibrin.However, a novel, additional explanation for the low bleeding rate withM5 also came to light in this study [Gurewich et al. J Thromb Haemost.4: 1559-65 (2006)].

Zymography of plasma samples from dogs in the dose-finding phase inwhich higher infusion rates of M5 were used, and where non-specificactivation occurred, showed an unusual inhibitor complex with tcM5. Thiscomplex was also seen when tcM5 (but not M5) was incubated in vitro indog or human plasma. The inhibitor was identified as C1-inhibitor basedon its co-migration with a complex formed with purified C1-inhibitor andWestern blotting with specific antibodies. It was postulated thatendogenous C1-inhibitor helped confine tcM5 activity to the fibrin-clotenvironment, thereby limiting non-specific plasminogen activation andsparing hemostatic fibrin in these dogs [Gurewich et al. (2006), supra].In the present study, C1-inhibitor inhibition of tcM5 was furtherinvestigated and its effect on fibrin-specific and non-specificplasminogen activation by M5 was characterized in vitro.

SUMMARY OF THE INVENTION

ProuPA is unstable in plasma at therapeutic concentrations. A mutantform, M5, was developed to make prouPA less subject to spontaneousactivation in plasma during fibrinolysis. The spontaneous activation totcuPA preempted prouPA-mediated fibrinolysis at therapeuticconcentrations and seriously compromised prouPA in clinical trials.

Activation of M5 to tcM5 induced a higher catalytic activity than tcuPA,implicating an active site functional difference. Consistent with this,an unusual tcM5 complex with plasma C1-inhibitor was recently describedin dog and human plasma. The effect of C1-inhibitor on fibrinolysis andfibrinogenolysis by M5 is the subject of this study.

Zymograms of tcM5 or tcuPA incubated in plasma revealed prominenttcM5:C1-inhibitor complexes which formed within five minutes. Theinhibition rate by purified human C1-inhibitor (250 μg/ml) was aboutseven-fold faster for tcM5 than for tcuPA (10 μg/ml), andseveral-hundred fold faster than for tPA, an interaction that waspreviously reported [Huisman et al. Thromb Haemost. 73: 466-471 (1995)].C1-inhibitor's effect on the stability of M5 or prouPA was determined byincubating them in plasma at high concentrations (10-20 μg/ml) with andwithout C1 inhibitor supplementation. Above 10 μg/ml, depletion of allplasma plasminogen occurred, indicating plasmin generation andtcM5/tcuPA formation. With supplemental C1-inhibitor, the stability ofM5 was restored but not that of prouPA. Clot lysis by M5 with or withoutsupplemental C1-inhibitor showed no attenuation of the rate offibrinolysis, whereas fibrinogenolysis was prevented by C1-inhibitor.Furthermore, due to higher dose tolerance of M5 with C1-inhibitor, therate of fibrin-specific lysis reached that achievable by nonspecificfibrinolysis without inhibitor. Plasma C1-inhibitor stabilized M5 in itsproenzyme configuration in plasma by inhibiting tcM5 and therebynon-specific plasminogen activation. At the same time, fibrin-specificplasminogen activation remained unimpaired. This unusual dissociation ofeffects by this plasminogen activator:inhibitor interaction isunprecedented and has significant implications for improving the safetyand efficacy of fibrinolysis.

A number of related aspects are described in detail in the followingsections.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1. Zymograms of tcM5 (5 μg/ml) (A) or tcuPA (5 μg/ml) (B) incubatedin pooled bank plasma for 0-60 min. The inhibitor complex at the top,forming within 5 min with tcM5, corresponds to C1 inhibitor, asevidenced by the last lane (C1 I) of an incubation (60 min) mixture ofpurified C1-inhibitor (250 μg/ml) and tcM5 or tcuPA. With tcuPA (B)there is more free enzyme seen and the complex is barely visible,reflecting its slower inhibition rate compared with tcM5 (A). The secondplasma inhibitor appearing at ˜115 kDa corresponds to antithrombin, aknown inhibitor of tcuPA.

FIG. 2. Zymograms of 120 min incubation mixtures of 10 μg/ml tcM5 (A) ortcuPA (B) with purified C1-inhibitor (250 μg/ml). The more rapidinhibitor complexation by tcM5 corresponds to the more rapid quenchingof activity shown in FIG. 3. The minor lower molecular weight lysisbands seen below the two enzymes correspond to by-products of theplasmin activation of the single chain proenzyme forms.

FIG. 3. The kinetics of tcM5 (diamonds) or tcuPA (circles) inhibition byC1-inhibitor from the incubation mixtures shown in FIG. 2. At the timepoints, uPA activity was measured with chromogenic substrate (S-2444).The points graphed are the means of two experiments (error bars aresmaller than the symbols; the R2 of the curves was 0.987 for tcM5 and0.997 for tcuPA). The data were fitted by computer to a non-linearregression for first order logarithmic decay.

FIG. 4. The effect of C1-inhibitor (250 μg/ml) when added to bank plasmaon plasminogen preservation in the presence of M5 (10, 15 or 20 μg/ml)or prouPA (10 μg/ml) incubated 4h in plasma. Plasma plasminogenremaining (% of baseline) is represented on the ordinate axis. As shown,supplementation (+) of the plasma with the inhibitor significantlyreduced plasminogen depletion by M5 at all doses but not by prouPA atthe dose used.

FIG. 5A. Lysis curves determined from release of D-Dimer from clots in aplasma milieu with (+) or without (−) supplemental C1-inhibitor (250μg/ml) and containing S or 10 μg/ml M5. As shown, the presence of theinhibitor did not attenuate the rate of fibrinolysis.

FIG. 5B. Fibrinogen concentrations remaining at the end of each clotlysis from 5A expressed as % of baseline. At 10 μg/ml of M5 (10−) therewas loss of almost all the fibrinogen, reflecting its degradation.However, with supplemental C1 inhibitor (10+) this did not occur.

FIG. 6A. Activity against C1 esterase chromogenic substrate (SpectrozymeC1-E) (open symbols) by 0-15 μg/ml of tcuPA or tcM5, amount adjusted togive comparable uPA substrate (S-2444) (solid symbols) activity. Asshown, tcM5 had less C1 esterase-like activity than tcuPA. (mΔA/min isthe change in milli-absorbance units (A405) with time, reflecting therate of conversion of chromogenic substrate to product.)

FIG. 6B. Reducing SDS-PAGE (Coomassie stained) of a 6 h incubationmixture of C4 (480 μg/ml) with buffer (lane 2), tcuPA (lane 3), tcM5(lane 4) or plasmin (lane 5) (10 μg/ml each). Molecular weight markersare in lane 1. The positions of the α, β, and γ chains of C4 and of theuPA B-chain (lanes 3 and 4) are shown on the right. A faint band isdiscernable between the α and β chains of C4 in lanes 3 and 4,consistent with a shift of a trace amount of the unchain by release ofthe anaphylatoxin peptide. By contrast, a gross degradative effect,particularly of the α-chain, is seen in lane 5.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a novel method of reducing bleedingduring fibrinolysis treatment and improving the rate of clot lysis. Themethod is based on the discovery that C1-inhibitor has the ability toinhibit plasminemia by inhibiting the two-chain prourokinase plasminogenactivator mutant tcM5. The inhibition rate of this interaction issufficient to prevent non-specific plasminogen activation but notfibrin-specific plasminogen activation.

ProuPA is a thrombolytic drug with the undesirable side effect of beingvulnerable to spontaneous activation in plasma during therapeuticfibrinolysis. M5 is a single site mutant of prouPA developed to limitthis non-specific effect and thereby to make fibrinolysis morefibrin-specific and to allow the physiological properties of prouPA tobe retained at therapeutic doses. The plasminogen activator, M5, differsfrom the primary sequence of prouPA by a single amino acid substitutionat position 300, where the amino acid Lysine has been replaced byHistidine (Lys 300→His) in a flexible loop region within the catalyticdomain of single-chain prouPA. This residue exchange lowered theactivator's intrinsic, single-chain activity by five-fold and made itmore stable in plasma to a corresponding degree [Liu, et al. (1996),supra]. After plasmin-activation to tcM5, the catalytic activity of tcM5was found to be higher than that of tcuPA [Sun et al. J Biol. Chem. 272:23818-23823 (1997)], implicating an unanticipated functional differencein their two-chain catalytic sites as well. The present findings, thatC1-inhibitor quenches the activity of tcM5 significantly moreeffectively than that of tcuPA, are consistent with such a difference,but were entirely unanticipated since no differences in inhibition byplasminogen activator inhibitor-1 (PAI-1) had previously been found.

C1-inhibitor is previously unknown as a plasma inhibitor of tcuPA.C1-inhibitor is a 104 kDa serine protease inhibitor with a normal plasmaconcentration of about 250 μg/ml and a half life of about 28 hours.Deficiency of this protein has been associated with a disease calledhereditary angioedema. C1-inhibitor has long been administeredclinically for the treatment of hereditary angioedema.

As discussed in the Background of the Invention section, ProuPA is aplasminogen activator that is subject to spontaneous activation inplasma at therapeutic concentrations due to its relatively highintrinsic catalytic activity. Plasmin then converts prouPA into tcuPA.Since tcuPA is a non-specific plasminogen activator, non-specificplasmin generation results in non-specific conversion of prouPA to tcuPAand loss of prouPA's physiological fibrin-specificity and associatedproperties. This includes the selective activation of plasminogen boundto partially degraded fibrin clots rather than intact fibrin clots, thelatter corresponding to hemostatic fibrin. M5 has only one-fifth theintrinsic catalytic activity of prouPA and therefore retains itsproenzyme form at therapeutic concentrations, and when used to lyseintravascular blood clots, M5 largely spares hemostatic fibrin, sincethis corresponds to intact fibrin. For the present invention,experiments were performed in vitro in human plasma. The actions of M5were studied in comparison to prouPA, its parent molecule, and tPA,currently the most commonly used thrombolytic drug.

The serine proteases tPA and prouPA are both natural plasminogenactivators, and both induce fibrin-specific lysis at limited doses bypreferentially activating fibrin-bound plasminogen over freeplasminogen. However, distinctly different mechanisms are responsiblefor this phenomenon. Each activator targets a different fibrin-boundplasminogen. The activator tPA is a single-chain enzyme with a highaffinity for a specific binding site on fibrin, where tPA forms aternary complex with an adjacent plasminogen [Hoylaerts et al., J Biol.Chem. 257: 2912-2919 (1982)]. This plasminogen is bound to an internallysine binding site (Lys-157) in the Aα chain of the D-region of fibrin[Nieuwenhuizen W et al., Biochim Biophys Acta. 748: 86-92 (1983)]. Inthe presence of fibrin fragment D binding site, which is constitutive ofintact fibrin, plasminogen activation by tPA is promoted by as much as1,000-fold [Petersen et al., Biochim Biophys Acta. 952: 245-254 (1988)],reflecting the importance of the ternary complex with intact fibrin fortPA.

By contrast, the single-chain prouPA has no fibrin affinity. Yet when aclot is added to plasma containing prouPA (or M5), local activation of afraction of the prouPA takes place on the fibrin surface and lysis istriggered [Liu et. al., Biochemistry 35: 14070-14076 (1996)]. Thissequence of events is facilitated by a conformational change inplasminogen for which prouPA (or M5) has high substrate affinity. Thischange occurs when plasminogen binds to its carboxy-terminal lysinebinding site in the E region of fibrin. In the presence of fibrinfragment E, plasminogen activation by single-chain prouPA/M5 is equal tothat of its two-chain derivative, tcuPA or tcM5, corresponding to aseveral hundred-fold promotion of its intrinsic activity [Liu andGurewich, Biochemistry 31: 6311-6317 (1992)].

Therefore, tPA and prouPA/M5 induce fibrin dependent plasminogenactivation involving selectively different fibrin-bound plasminogenmoieties. In the case of tPA, it is dependent on an internal lysineplasminogen binding site in the fibrin D region, whereas prouPA/M5 isdependent on carboxy-terminal lysine binding in the E region of fibrin.This difference is selective since there is little or no reciprocity. Ina purified system, plasminogen activation by tPA is promotedspecifically by fibrin fragment D and that by prouPA/M5 is promoted onlyby fibrin fragment E (Liu and Gurewich, J Clin Invest. 88: 2012-2017(1991)). Newly formed intact (hemostatic) fibrin contains only theinternal lysine plasminogen binding site in the D region of fibrin. Thecarboxy-terminal lysines in the E region are created only after plasmindegradation has occurred (Harpel et al., J Biol. Chem. 260: 4432-4440(1985)). This difference is evidenced by the lag phase which ischaracteristic of prouPA (or M5)-induced clot lysis in a plasma milieuand by the fact that the lag phase is substantially attenuated by gentlepre-treatment of the clot with plasmin, which creates the fibrinfragment E carboxy-terminal lysine plasminogen binding sites.Conversely, tPA-induced clot lysis in plasma has no lag phase and tPAlyses intact and degraded fibrin clots equally well under these sameconditions (Pannell et al., J Clin Invest. 81: 853-859 (1988)). Thus,intact fibrin is relatively resistant to lysis by prouPA/M5 whereas itis not resistant to tPA.

Hemostatic fibrin, consistent with its physiological function, isprotected from plasmin degradation by several physiological safeguards.These include the inhibition of free tPA (and tcuPA) by PAI-1 and theremoval of carboxy-terminal binding sites on fibrin bythrombin-activated procarboxypeptidase in plasma (Hendriks et al., JClin Chem. Clin Biochem. 27: 277-280 (1989)). By contrast, when anintravascular thrombus forms and causes a vascular occlusion,physiological mechanisms for its degradation are triggered. Inparticular, there is a release of tPA from the vessel wall which, aidedby the local stasis, binds to the thrombus. Fibrin degradation isinitiated thus creating new carboxy-terminal lysine plasminogen bindingsites which facilitate lysis (Harpel et al., J Biol. Chem. 260:4432-4440 (1985)), particularly by prouPA/M5.

The presence of the fibrin E region plasminogen binding sites in anintravascular thrombus but not in hemostatic fibrin provides anexplanation for why effective thrombolysis by M5 spares hemostaticfibrin, but only if systemic tcM5 generation is avoided. In contrast,the D region ternary complex plasminogen binding site is present inhemostatic fibrin, making it more vulnerable to lysis by tPA. Thisconcept is consistent with tPA-associated bleeding which has been shownto have a low correlation with fibrinogen degradation, a sign ofnon-specificity (Montoney et al., Circulation 91: 1540-1544 (1995)).This is because this bleeding is related to direct lysis of fibrin at ahemostatic site. By contrast, bleeding with prouPA is directlycorrelated with non-specificity, which leads to a generalizedhemorrhagic state.

In a study of rebleeding from hemostatic sites during thrombolytictreatment of dogs, the findings of U.S. application Series No.11/472,607 indicated a relative sparing of hemostatic versusintravascular fibrin when M5 was used and suggested that these twofibrins are functionally distinct with respect to their sensitivity tolysis by M5. In the study, M5 induced lysis was comparable in efficacy,but caused ten-fold less bleeding than tPA induced lysis, consistentwith a sparing of hemostatic fibrin. The study further showed that whenthe enzymes tcM5 and tcuPA were each incubated in vitro in either humanor dog plasmas, an inhibitor complex consistent with C1-inhibitor (˜150kDa) appeared within minutes of the incubation of tcM5 in plasma. Thesparing of hemostatic fibrin was postulated to be both becauseplasminogen activation by M5 was not promoted by intact fibrin andbecause of the efficient inhibition of tcM5 by plasma C1-inhibitor,which prevented non-specific plasmin generation.

The present invention is concerned with the effect of C1-inhibitor onfibrinolysis and fibrinogenolysis by M5. As discussed in theExemplification section which follows, C1-inhibitor formed thepredominant complex with tcM5 in plasma (FIG. 1A), in contrast to theresults with tcuPA, suggesting that C-1 inhibitor helps preventnon-specific plasmin generation by M5/tcM5. During thrombolysis, plasmingeneration must be confined to the fibrin clot environment, if not,plasminogen in the ambient plasma will be activated and the proenzyme(M5 or prouPA) converted to the two-chain enzyme. Only plasma inhibitorscan confine tcM5 (or tcuPA) activity to the clot environment. Plasmainhibitors are essential factors in the fibrin-specific mechanism ofaction of prouPA or M5 and for retaining the proenzyme state of prouPAand M5 in an environment in which plasminogen is present.

As discussed in the Exemplification section, tcM5 and tcuPA at identicalconcentrations were incubated with exogenous C1-inhibitor in plasma. Thezymograms show a rapid and progressive loss of the tcM5 free enzymeassociated with the appearance of prominent inhibitor complexes (FIG.2A). In the present comparative study, tcM5 was more efficientlyinhibited in plasma than tcuPA, mostly due to its formation of a complexwith C1-inhibitor. Only a very faint C1-inhibitor complex with tcuPA wasseen (FIG. 2B). There was essentially complete inhibition of tcM5 within60 min, whereas 30% of the tcuPA activity remained even after 3 h ofincubation. In a purified system, the inhibition rate of C1-inhibitorwas about seven-fold greater against tcM5 than tcuPA. As shown in Table1, the inhibition of tcuPA was about 100-fold faster than thatpreviously described for tPA. The inhibition of tcM5 in plasma is whatlimits the cyclic reactions which would otherwise result in plasmingeneration and lead to more tcM5 and plasmin generation, and bleeding.The efficient inhibition of tcM5 by C1-inhibitor can, therefore,contribute significantly to confining tcM5 generation to theintravascular clot environment, thereby protecting the more remotehemostatic fibrin.

As discussed in the Exemplification section, when plasma wassupplemented with C1-inhibitor (250 μg/ml), the M5 concentrationthreshold at which tcM5 conversion and non-specific plasminogenactivation occurred was substantially raised (FIG. 4). Therefore,C1-inhibitor, by inhibiting tcM5, effectively helped stabilize M5 inplasma and allowed a higher concentration of M5 to be tolerated withoutcompromising fibrin-specificity. By contrast, as shown by the last twobars in FIG. 4, C1-inhibitor supplementation had no attenuating effecton plasminogen activation of prouPA at the high concentrations used inthese experiments.

When fibrin-dependent plasminogen activation was tested by measuring therate of clot lysis by M5, no inhibition by supplemental C1-inhibitor wasobserved (FIG. 5A). However, fibrinogenolysis, reflecting non-specificplasminogen activation, was completely prevented (FIG. 5B). Thisdifference between the inhibition of non-specific plasminogen activationand fibrin-dependent plasminogen activation (fibrinolysis) wasunexpected and unpredictable since previous studies with prouPA andsupplemental PAI-1 showed that this inhibitor inhibited both reactionsto a comparable degree.

These results of the present study make clear, and the present inventionincludes, methods of administering an amount of exogenous C1-inhibitoralong with M5 during fibrinolysis treatment that limit non-specificplasminogen activation in the blood and reduce bleeding complications ofthrombolytic therapy. An amount of M5 effective to cause lysis of anocclusive blood clot should be administered along with an amount ofexogenous C1-inhibitor sufficient to limit non-specific plasminogenactivation in blood. Moreover, since C1-inhibitor permits higher dosesto be safely administered, faster rates of lysis are possible, as shownin FIG. 5A. The M5 mutant is administered as a thrombolytic agent in thesame way as prouPA and tcuPA. M5 is mixed with a pharmaceuticallyacceptable carrier, e.g., saline, and administered by intravascular,e.g., intravenous or intra-arterial injection. The present inventionincludes methods where M5 may be injected as a bolus of approximately 20to 60 mg, or may be infused intravenously at a rate of 40-80 mg/hour.Since M5 has far greater plasma stability than native prouPA and is lesslikely to induce non-specific plasminogen activation, higher dosages,e.g., infusions of up to 200 mg/hour may also be used.

In another embodiment, the present invention includes a method ofinhibiting the enzymatic activity of tcM5. As is detailed in theExemplification, an amount of exogenous C1-inhibitor sufficient to limitthe formation of tcM5 from M5 activation should be administered to apatient desiring to limit the activity of tcM5.

In another embodiment, the present invention includes a method ofincreasing the plasma stability or inertness of M5 during fibrinolysistreatment. M5's stability is increased by administering exogenousC1-inhibitor sufficient to establish a C1-inhibitor concentration withinthe range of 1.5 to 4, preferably 2 to 3, times the concentration ofaverage normal endogenous C1-inhibitor. The C1-inhibitor inhibitsnon-specific plasminogen activation of tcM5 without inhibiting clotlysis or fibrin-specific plasminogen activation by tcM5.

The present invention includes the treatment of a patient with M5 and anamount of exogenous C1-inhibitor sufficient to establish C1-inhibitorconcentrations greater than physiological levels in the plasma of thepatient. There is a range of normal physiological levels. Average normalphysiological levels are about 250 μg/ml. Individuals at the lower endof the range, especially those being treated for ischemic stroke, mayhave physiological levels of C1-inhibitor as low as 150 μg/ml. Those inthe high physiological range may have native levels of C1-inhibitor ashigh as 450 μg/ml. Those at the lower end would be more vulnerable tobleeding complications related to M5 and so their need forsupplementation would be greater. The concentrations established inplasma during treatment should be within the range of 1.5 to 4,preferably 2 to 3, times that of average physiological levels orapproximately 0.5 g/l to 1.5 g/l. As is detailed in the Exemplificationsection, a C-1 inhibitor supplementation of 0.25 g/l was effective inpromoting the plasma stability of M5, raising the M5 thresholdconcentration at which non-specific plasminogen activation occurs, andsignificantly inhibiting the non-specific activity of tcM5.

At the same time that M5 fibrinolysis was not inhibited,fibrinogenolysis was completely inhibited by supplementation withC1-inhibitor. Therefore, C1-inhibitor restored fibrin-specificity to themore rapid clot lysis rate otherwise achievable only at non-specificdoses of the activator, i.e., at which fibrin degradation by excessplasmin is the rate-limiting factor. As a result, the dose-limit forfibrin-specific clot lysis was raised. In fact, the rate achieved withsupplemental C1-inhibitor was equivalent to that achievable bynon-specific clot lysis, i.e., that rate possible when plasmin itself israte limiting. Since all plasminogen activators lyse fibrin indirectly,the maximal rate of fibrinolysis possible is that at which plasmindegradation of fibrin becomes the rate limiting step in the lysis.C1-inhibitor supplementation made possible a maximal fibrinolysis rateby M5 in vitro without sacrificing fibrin-specificity. Therefore, thepresent invention also includes methods of accelerating the rate of clotlysis, during thrombolysis treatment in a patient, while preventingfibrinogen degradation. The methods include administering M5 in anamount sufficient to establish concentrations of 10-15 μg/ml in plasmatogether with exogenous C1-inhibitor in an amount sufficient toestablish a concentration within the range of 1.5 to 4, preferably 2 to3, times physiological levels in the plasma of the patient. The methodsinclude the case wherein the level of C1-inhibitor established is about500-750 μg/ml in the plasma of the patient.

The methods of the present invention include the administration ofexogenous C1-inhibitor mixed with a pharmaceutically acceptable carrierand administered as a bolus wherein the level of C1-inhibitor in theplasma of the patient is brought into the high physiological range.Included is the method wherein the level of C1-inhibitor established inthe plasma of the patient is about 750 μg/ml. The methods includeadministering the bolus of exogenous C1-inhibitor prior to thrombolysiswith M5. The half-life of native C1-inhibitor is about 28 hours. That ofrecombinant C1-inhibitor can be much shorter, such as three hours. Theappropriate amount of exogenous C1-inhibitor to administer depends onits half-life. A good quantity of exogenous C1-inhibitor to administeris 0.5 gm as a bolus or by intravenous infusion.

Native C1-inhibitor is used to treat hereditary angioedema. For thepurposes of thrombolysis with M5, the longer half-life of nativeC1-inhibitor is not necessary because the C1-inhibitor is needed for atmost 90 minutes. Therefore a recombinant C1-inhibitor may be used,including that made in yeast or E. coli. Recombinant forms may benon-glycosylated or glycosylated differently than the heavilyglycosylated native C1-inhibitor. The differences in -glycosylationaffect metabolism and may not be suitable for angioedema patients forwhich a long half-life may be optimal. However, thrombolysis is an acutetherapy so that a much compromised half-life for C1-inhibitor would bewell-suited for this application. C1-inhibitor enzymatic inhibition isdetermined by the protein rather than its glycosyl moiety. Both thenative and the recombinant forms of C1-inhibitor can be used to inhibittcM5 and thus accelerate the rate of blood clot lysis duringthrombolysis while preventing fibrinogen degradation. Therefore thepresent invention includes methods wherein the exogenous C1-inhibitoradministered is of recombinant origin or of native origin. The methodsinclude the case wherein the exogenous C1-inhibitor is non-glycosylatedor differently glycosylated from the native form.

C1-inhibitor also had a modest effect on non-specific plasminogenactivation by prouPA/tcuPA, but only at much lower concentrations ofthem than those used in the present study. This is consistent with itsweaker inhibition, which was, nevertheless, much greater than thatreported for tPA [Huisman et al. Thromb Haemost. 73: 466-471 (1995)].The principal plasma inhibitor of tPA and tcuPA is PAI-1. However,raised levels of PAI-1 have been associated clinically with impairedfibrinolysis [Juhan-Vague et al. Thromb Res. 33: 523-530 (1984); Meadeet al. Lancet. 342: 1076-1079 (1993)]. Similarly, in studies of theeffect of PAI-1 supplementation (25-100 ng/ml) on clot lysis by prouPAin a plasma milieu, a dose-dependent inhibition of clot lysis took place(unpublished observations). These previous findings with PAI-1 are instark contrast to the present findings with C1-inhibitor, wherein clotlysis was not inhibited.

C1-inhibitor complexes were previously identified in the plasma of dogsgiven higher, non-specific doses of M5. It was postulated that thisinhibition of tcM5 by endogenous C1-inhibitor may have contributed tothe ten-fold lower blood loss associated with M5 compared with tPA inthe study [Gurewich et al. (2006), supra]. The present findings indicatethat if supplemental C1-inhibitor had been administered to these dogs,faster lysis rates from higher doses accompanied by the same lowbleeding incidence would have been achieved.

The present invention includes a method of preventing side effects, suchas bleeding, during fibrinolysis treatment in a patient by administeringM5 along with exogenous C1-inhibitor. The M5 is administered in anamount sufficient to cause a maximal rate of lysis of an occlusive bloodclot and the exogenous C1-inhibitor is administered in an amountsufficient to limit non-specific plasminogen activation by M5. TheC1-inhibitor inhibits non-specific plasminogen activation and bleeding.The maximal rate of lysis is the rate at which the plasmin degradationof fibrin, rather than the plasminogen activation by M5, is the ratelimiting step in clot lysis. Plasminogen activators, such as M5, areindirect lytic agents. They activate plasminogen which becomes plasmin.The plasmin then lyses fibrin. If the plasmin is the rate limiting step,the two-step reaction cannot go faster even if more plasminogenactivator is added. Using supplemental C1-inhibitor allows the maximumrate of clot lysis by M5 to take place without risking massivenon-specific plasminogen activation and its side effects. With M5 andC1-inhibitor, because of the action of C1-inhibitor on tcM5, the maximumrate of clot lysis can be achieved safely. C1-inhibitor preventsbleeding and at the same time allows for a more rapid rate ofthrombolysis. In vivo the maximum rate of lysis can be achieved by M5 ata dose of about 150 mg infused over 60-90 minutes.

The methods of the present invention include methods of increasing thedose-range of fibrin-specific lysis by M5 in a patient. Included methodscomprise administering exogenous C1-inhibitor in an amount sufficient toprevent non-specific plasminogen activation by M5. Included is themethod wherein the exogenous C1-inhibitor administered establishes aconcentration of C1-inhibitor, in the plasma of the patient, that iswithin the range of 1.5 to 4, preferably 2 to 3, times that of averagenormal physiological levels.

The dissociation observed between the inhibition by C1-inhibitor ofnonspecific and fibrin-specific plasminogen activation is consistentwith the two different rates of plasminogen activation which areinvolved. Fibrin bound plasminogen is activated more rapidly than freenative plasminogen in plasma. In the case of prouPA/M5 it has been shownthat plasminogen activation is promoted more than two-hundred. fold byfibrin, specifically fibrin fragment E [Liu et al. Biochemistry 31:6311-6317 (1992)]. As a consequence, the C1-inhibitor inhibition rate oftcM5 is sufficient to prevent non-specific plasminogen activation butinsufficient to interfere with the more rapid activation of fibrin-boundplasminogen.

In conclusion, C1-inhibitor was more reactive against tcM5 than tcuPA,and when added to plasma it prevented non-specific plasmin generation byM5 at high fibrinolytic concentrations. Since plasminemia can causebleeding [Rao et al. (1988), supra; Fennerty et al. (1989), supra],clotting [Hoffmeister et al. Thromb Res. 103: S51-S55 (2001)], the“plasminogen steal” phenomenon [Torr et al. J Amer Coll Cardiol. 19:1085-1090 (1992)], and complement activation [Bennett et al. J Amer CollCardiol. 10: 627-632 (1987)], limiting non-specific plasmin generationwithout interfering with fibrinolysis is of special clinical interest.An inhibitor that controls this dose-related plasminogen activator sideeffect has the potential to optimize the lysis rate and minimize sideeffects, thereby helping overcome current limitations of therapeuticthrombolysis. Prevention of these consequences is unique to M5 withC1-inhibitor.

EXEMPLIFICATION

Materials

Recombinant Lys3000→His mutant (M5) prouPA expressed in Escherichia coli(E. coli) was prepared as previously described [Liu et al. (2002),supra] and obtained from Dr. Paolo Sarmientos at Primm (Milan, Italy).Recombinant prouPA expressed in E. coli was obtained from LandingScience and Technology Company, Nanjing, China. Human C1-inhibitorconcentrate prepared from human plasma was kindly supplied by ZLBBehring GmbH (Marburg, Germany). Human Complement factor four (C4) wasobtained from Calbiochem, Torry Pines, Calif. Chromogenic substrates foruPA (S-2444) and plasmin (S-2251) were obtained from DiaPharma (WestChester, Ohio, USA). The chromogenic substrate for C1 esterase(Spectrozyme C1E) was obtained from American Diagnostica, Stamford,Conn.

Methods

Fibrinogen was measured as thrombin clottable protein. Plasma wasdiluted with 2 vol 0.06 M sodium phosphate, pH 6.1. One volume ofthrombin (100 NIH U/ml, ThromboMax from Sigma, St Louis, Mo., USA) wasadded, mixed, and incubated for 30 min at 37° C. The clot was wound ontoa wooden stick to express the diluted serum, rinsed in 5 ml of thebuffer, and deposited into a tube containing 1 ml of 5% NaOH. Afterboiling for 1 min, the clot was dissolved and the protein measuredspectrophotometrically at 280 nm.

Zymography was performed by the method of Granelli-Piperno and Reich [JExp Med. 148: 223-234 (1978)] as modified by Vassalli et al. [J Exp Med.159: 1653-1658 (1984)] with sodium dodecyl sulfate polyacrylamide gelelectrophoresis (SDS-PAGE) according to Laemmli. After electrophoresis,the gel washed with agitation for 2 h in 2.5% Triton X-100 in water,followed by 1 h in 0.1 M Tris-HCl (pH 8.0) and then placed on anunderlay consisting of 0.8% agarose (Agarose low melting, FisherBiotech, Kent City, Mich., USA), casein (2% w/v; Carnation non-fat drymilk, Nestle, Glendale, Calif., USA) and plasminogen (20 μg/ml) in 0.1 MTris HCl (pH 8.0) With incubation, the electrophoretic bands ofplasminogen activator produce a clear zone in the white casein.Plasminogen activator inhibitor complexes become active in this systemand also show up as lytic zones.

Zymograms of the Two-Chain Activators in Plasma

The single-chain forms of M5 and of uPA were converted to two-chain byincubation with 0.2 μM plasmin (American Diagnostica, Greenwich, Conn.,USA) for 45 min at 37° C. in 0.05 M Tris-HCl, 0.1 M NaCl, 0.010%Tween-80, 10 mg/ml BSA as previously described [Pannell et al. Blood.69:22-26 (1987)]. These were added to human bank plasma (5 μg/ml) andincubated at 37° C. for 1 h with time point samples taken for zymography(FIG. 1).

Inhibitor Complexes in Plasma and with Purified C-Inhibitor

FIG. 1 shows zymograms of plasma in which equal amounts (5 μg/ml) oftcM5 (A) or tcuPA (B) were incubated (0-60 min). With tcM5 (A), therewas a progressive loss over time of the uncomplexed enzyme associatedwith the appearance within 5 min and progressive increase of lysis bandsat ˜150 kDa, corresponding to complexes with C1-inhibitor. The last laneshows the complex which was formed when purified C1-inhibitor wasincubated for 1 h with tcM5 (5 μg/ml) migrating in the same positionWith tcuPA (B), the uncomplexed enzyme persists in the plasma for alonger time and the C1-inhibitor complexes appear more slowly and aremuch less apparent. The complex with purified C1-inhibitor (last lane)is too faint to be visible on the print. The lower MW inhibitor complexin plasma (˜115 kDa) is with antithrombin, a known plasma inhibitor oftcuPA [Murano et al. Blood 55: 430-436 (1980)]. This has about the sameintensity as that with C1-inhibitor with tcuPA (but not with tcM5).

On the zymograms, both the free tcM5 but especially the tcuPA, appear ashigher and lower molecular forms, the latter more degraded form is aninevitable by-product of the plasmin activation of their parentsingle-chain forms. Complexes with PAI-1 in the plasma are not visibledue to the negligible concentration of this inhibitor relative to thatof the activators.

C1-Inhibitor Inhibition of tcM5 and tcuPA

The two-chain forms of M5 and of uPA were incubated (10 μg/ml) withpurified C1-inhibitor (250 μg/ml) at 37° C. in 0.05 M Tris-HCl, 0.1 MNaCl, 0.01% Tween-80, 10 mg/ml BSA. Samples were taken at time pointsand assayed for remaining activity by chromogenic assay (S-2444) (FIG.2). The data were plotted directly (FIG. 3) and a non-linear regressionfor first-order logarithmic decay was performed using GraphPad Prism(version 3.03 for Windows, GraphPad Software, San Diego, Calif., USA) inorder to obtain the half-life (t_(1/2)) for inhibition. The pseudo-firstorder inhibition rate constant was calculated fromk′=0.693/(t_(1/2)×[tcuPA]).

FIG. 2A and B are zymograms of incubation mixtures of equal amounts oftcM5 or tcuPA incubated in buffer in the presence of purifiedC1-inhibitor (250 μg/ml), corresponding approximately to itsphysiological concentration. Similar to the findings in plasma, arelatively rapid and progressive loss of the tcM5 free enzyme was seenassociated with the appearance of prominent inhibitor complexes (FIG.2A). By contrast, with tcuPA the free enzyme persisted due to only amodest formation of inhibitor complexes taking place during theincubation, reflecting the differences in their inhibition rates (FIG.2B).

Kinetics of Inhibition by C1-Inhibitor

FIG. 3 shows the kinetics of inhibition of tcM5 compared with tcuPA inbuffer containing C1-inhibitor (250 μg/ml) and 10 μg/ml (a hightherapeutic concentration) of the two activators. At time points,synthetic substrate (S-2444) activity was measured and expressed aspercent of uPA activity remaining. As shown, inhibition of uPA activityoccurred at two very different rates. There was essentially completeinhibition of tcM5 within 60 min, whereas 30% of the tcuPA activityremained even after 3 h of incubation.

TABLE 1 Inhibition Kinetics. t_(1/2) k' (min) (M⁻¹ sec⁻¹) tcM5 10 5.78 ×10³ tcuPA 68 0.85 × 10³ tPA^(a) 0.008 × 10³  ^(a)For melanoma singlechain tPA from Murano et al., Blood 55: 430-436 (1980); adjusted tonormalize to the inhibitor concentration we used.

The inhibition rate of C1-inhibitor was about seven-fold greater againsttcM5 than tcuPA. Huisman et al. [Huisman et al. (1995), supra]previously reported that C1-inhibitor formed complexes with both singleand two-chain tPA, but these complexes formed more slowly. C1-inhibitorhas not previously been included among the plasma inhibitors of tcuPA[Murano et al. (1980), supra]. As shown in Table 1, the inhibition oftcuPA was about 100-fold faster than that previously described for tPAby Huisman et al. [Huisman et al. (1995), supra] (recalculated tonormalize to the inhibitor concentration we used).

Stability of M5 or prouPA in Plasma as a Function of SupplementalC1-Inhibitor

To determine the stability of the single chain forms of M5 and uPA inplasma, the M5 and prouPA were incubated (37° C. for 4 h) in plasma at arange of concentrations (10, 15, and 20 μg/ml) with and without extraC1-inhibitor added (250 μg/ml). Enzymatic activation of plasminogen wasdetermined by measuring the plasminogen remaining (FIG. 4) bychromogenic assay (S-2251) after its activation with Streptokinase (2500units/ml). C1-inhibitor also inhibits plasmin [Harpel. J Clin Invest.49(3): 568-75 (1970)] which potentially complicates the assay. However,it was determined that SK:plasmin complexes, which are generated forthis assay, are not inhibited by C1-inhibitor (unpublishedobservations).

Since prouPA is far less stable in plasma than M5, a separate studyusing far lower concentrations (2 and 4 μg/ml) incubated in plasma 2 hand 4 h±C1-inhibitor was also performed.

Promotion of M5 Stability in Plasma by C1-Inhibitor Supplementation

M5, like prouPA, is a single-chain zymogen which is activated byplasmin. Plasmin generation is triggered by the intrinsic activity ofthe proenzymes when they reach a certain threshold, such as attherapeutic concentrations. Conversion to the two-chain forms thenamplifies plasminogen activation. Although the intrinsic activity of M5is five-fold lower than that of prouPA [Liu, et al. (1996), supra],making its plasma stability or inertness that much greater, itnevertheless also has its concentration limits.

Therefore, the effect, of supplemental C1-inhibitor (250 μg/ml) added toplasma, on the concentration threshold at which instability occurs wasevaluated. M5 or prouPA (10, 15, and 20 μg/ml) were incubated in plasmafor 4 h with or without additional C1-inhibitor, after which the plasmaplasminogen remaining was measured.

As shown in FIG. 4, at an M5 concentration of 10 μg/ml, non-specificplasminogen activation began to occur (˜25% loss of plasminogen) after 4h, and at concentrations of 15 and 20 μg/ml, plasminogen activation byM5, as reflected by its depletion, was ˜85% and >90% respectively.However, with additional C1-inhibitor, plasminogen depletion wasprevented at the 10 μg/ml M5 concentration, and at 15 and 20 mg/ml,reduced to ˜30% and ˜60% respectively. Therefore, C1-inhibitorsupplementation was effective in promoting the plasma stability of M5 byraising the threshold concentration at which non-specific plasminogenactivation occurred.

By contrast, as shown by the last two bars in FIG. 4, C1-inhibitorsupplementation had no attenuating effect on plasminogen activation ofprouPA at the high concentrations used. At much lower concentrations (2,4, and 6 μg/ml) of prouPA, however, some attenuation of non-specificplasminogen activation by C1-inhibitor was seen (data not shown).

Fibrin-Specific Clot Lysis as a Function of Supplemental C1-Inhibitor

Clots were formed from 0.2 ml bank plasma by recalcification (35 mM)with the addition of a trace of thromboplastin and incubated at 37° C.for 1 h and overnight at room temperature. The following day, the clotswere placed into 2.5 ml of bank plasma and M5 was added at 5 or 10μg/ml. Lysis was determined by measuring the D-Dimer concentration inplasma samples removed at time intervals (FIG. 5A). The D-Dimerdeterminations were made independently by Dr. Gregory Gauvin, Mt AuburnHospital, Cambridge, Mass. using a Beckman ACL 8000 analyzer. Afterlysis had gone to completion, aprotinin (500 KIU/ml) was added and thefibrinogen concentration determined and compared with that from abaseline sample (FIG. 5B).

The Effects of C1-Inhibitor on Clot Lysis and Fibrin Specificity

The attenuation of non-specific plasminogen activation by C1-inhibitorsuggested that fibrin-dependent plasminogen activation and fibrinolysismight also be inhibited. This was anticipated from the clinicalexperience with PAI-1 in which higher levels have correlated clinicallywith fibrinolytic resistance, and also from our own laboratory findingsin which a PAI-1 dose-dependent inhibition of clot lysis in a plasmamilieu by prouPA was previously found (unpublished observations).

FIG. 5A shows representative clot lysis curves measured by the releaseof D-Dimer from a standardized plasma clot. Lysis induced by 5 or 10μg/ml of M5 in plasma went to completion in 1½ and 2 hours,respectively, either with (open symbols) or without (closed symbols)C1-inhibitor supplementation (250 μg/ml). No detectable attenuation ofthe rate of M5-mediated fibrinolysis by the inhibitor was found(experiments done in triplicate), indicating that C1-inhibitor did notinhibit fibrin-dependent plasminogen activation.

By contrast, as seen in FIG. 5B showing the fibrinogen concentrations(as % of baseline) at the end of each clot lysis experiment,fibrinogenolysis was completely inhibited by supplementation withC1-inhibitor (indicated by the + symbol). Therefore, C1-inhibitorcompletely restored fibrin-specificity to the more rapid clot lysis rateotherwise achievable only at non-specific doses of the activator, i.e.,at which fibrin degradation by excess plasmin is the rate-limitingfactor.

Since plasmin is the common denominator of all plasminogen-activatormediated lysis, the findings that the fibrin-specific and non-specificrates (when plasmin is in excess), were equivalent are of specialinterest. They suggest that C1-inhibitor supplementation made a maximalfibrinolysis rate by M5 possible in vitro without sacrificingfibrin-specificity.

Evaluation of C1 Esterase Activity

Since tcM5 was inhibited by the principal inhibitor of C1 esterase, thepossibility that it may itself have some intrinsic C1 esterase activitywas tested. Equal amounts (10 μg/ml) of tcM5 and tcuPA, adjusted to haveequivalent activities against the uPA chromogenic substrate (S2444),were tested against the tripeptide chromogenic substrate SpectrozymeC1-E (480 μg/ml) (FIG. 6A).

Since Complement factor 4 (C4) is the natural substrate for C1 esterase,release of the ˜9 kDa peptide from the α-chain of C4 by the activators,using plasmin as a positive control, was also evaluated. A mixture of 10μl of tcM5, tcuPA, plasmin (10 μg/ml) or buffer were incubated (37° C.)for 6 h with 40 μl C4 (480 μg/ml). Each of the incubation mixtures withC4, except plasmin, also contained aprotinin (100 KIU/ml). At the end ofincubation, the mixtures were analyzed by SDS-PAGE under reducingconditions (FIG. 6B).

FIG. 6A shows that at concentrations of tcuPA and tcM5 which wereequivalent against uPA chromogenic substrate (solid symbols), tcuPA hadmore activity against C1 esterase chromogenic substrate than did tcM5(open symbols). A comparable difference in the same direction was foundagainst the more general substrate, benzoyl-argininyl methyl ester(Sigma) (data not shown).

FIG. 6B shows an SDS PAGE under reducing conditions of the 6 hincubation mixtures of C4 with the following: buffer (lane 2), tcuPA(lane 3), tcM5 (lane 4) or plasmin (lane 5) (10 μg /ml). A faint band isdiscernable between the α and β chains of C4 in lanes 3 and 4,consistent with a shift of a trace amount of the α-chain by release ofthe peptide after a 6 h incubation with a high therapeutic concentrationof either tcuPA or tcM5. By contrast, plasmin had a gross degradativeeffect, particularly of the α-chain.

The effect of plasmin is consistent with those reports in whichcomplement activation and anaphylatoxin generation were found associatedwith therapeutic thrombolysis. This potentially deleterious side effectof plasmin further underscores the importance of limiting non-specificplasmin generation during fibrinolysis as much as possible.

C1-inhibitor is a major inhibitor of the complement pathway,specifically C1 esterase, but also has a number of other target serineproteases, including Factors XIIa, XIa, kallikrein, and tPA (for reviewsee Ref. 17). The present findings indicate that tcuPA, and especiallytcM5, need to be added to the list.

Due to the unusual interaction of tcM5 with C1-inhibitor, the questionof whether tcM5 may itself have C1 esterase activity was raised. Theactivation of the complement system can cause damage to cells. Whencompared with an equivalent amount of tcuPA, tcM5 had, in fact, lessactivity against a C1 esterase synthetic substrate (FIG. 6A). Againstits natural substrate, C4, both tcuPA and tcM5 at high therapeuticconcentrations had a comparable effect consistent with release of atrace amount of anaphylatoxin after a six hour incubation. By contrast,plasmin induced a major degradation (FIG. 6B), consistent with reportsof complement activation and anaphylatoxin generation during therapeuticthrombolysis [Bennett et al. (1987), supra]. This data shows that M5 issafe and underscores the importance of limiting non-specific plasmingeneration, as has been demonstrated with supplemental C1-inhibitor withM5.

1. A method of accelerating the rate of blood clot lysis whilepreventing fibrinogen degradation in a human patient, comprising: a)providing M5 and exogenous C1-inhibitor; b) administering to a humanpatient an amount of M5 sufficient to establish M5 concentrations of10-15 μg/ml in the plasma of the patient; and c) administering, at thesame time or before step b), an amount of exogenous C1-inhibitorsufficient to establish a concentration of C1-inhibitor, in the plasmaof the patient, that is within the range of 1.5 to 4 times averagenormal physiological levels; wherein non-specific plasminogen activationby M5 is prevented.
 2. The method of claim 1, wherein the C1-inhibitoris administered in an amount sufficient to establish a concentrationthat is within the range of 2 to 3 times average normal physiologicallevels.
 3. The method of claim 1 wherein the C1-inhibitor is mixed in apharmaceutically acceptable carrier and administered as a bolus.
 4. Themethod of claim 3 wherein the bolus is administered at the same time asM5.
 5. The method of claim 1 wherein the C1-inhibitor is either ofrecombinant origin or of native origin.
 6. The method of claim 5 whereinthe C1-inhibitor is of recombinant origin and is non-glycosylated ordifferently glycosylated from the native form.
 7. A method ofadministering a thrombolytic to a human patient without inducingnon-specific plasminogen activation, comprising: a) providing thethrombolytic M5 and exogenous C1-inhibitor; b) administering an amountof exogenous C1-inhibitor sufficient to establish a concentration ofC1-inhibitor, in the plasma of the human patient, that is within therange of 1.5 to 4 times average normal physiological levels; and at thesame time or after step b) c) administering to the human patient anamount of M5 sufficient to establish M5 concentrations of 10-15 μg/ml inthe plasma of the human patient; and wherein non-specific plasminogenactivation by M5 is prevented.
 8. The method of claim 7 wherein saidC1-inhibitor is administered at the same time as thrombolysis with M5.9. The method of claim 7, wherein the C1- inhibitor is administered inan amount sufficient to establish a concentration that is within therange of 2 to 3times average normal physiological levels.
 10. A methodof administering a thrombolytic to a human patient while inhibitingnon-specific plasminogen activation, comprising: a) providing thethrombolytic M5 and exogenous C1-inhibitor; b) administering an amountof exogenous C1-inhibitor sufficient to establish a concentration ofC1-inhibitor, in the plasma of the human patient, that is within therange of 1.5 to 4 times average normal physiological levels; and c)administering, after or at the same time as step b), to a the humanpatient an amount of M5 sufficient to establish M5 concentrations of10-15 μg/ml in the plasma of the patient; and wherein non-specificplasminogen activation by M5 is inhibited, without inhibiting clot lysisor fibrin-specific plasminogen activation of M5.